Question: The real number $x$ satisfies $x^2 - 5x + 6 < 0.$  Find all possible values of $x^2 + 5x + 6.$
The inequality $x^2 - 5x + 6 < 0$ factors as $(x - 2)(x - 3) < 0,$ so the solution is $2 < x < 3.$  Since $x^2 + 5x + 6$ is increasing on this interval, we have that
\[x^2 + 5x + 6 > 2^2 + 5 \cdot 2 + 6 = 20\]and
\[x^2 + 5x + 6 < 3^2 + 5 \cdot 3 + 6 = 30.\]Therefore, the set of possible values of $x^2 + 5x + 6$ is $\boxed{(20,30)}.$